<p>Don't crawl these:</p>
<ul>
  <li><a href="http://webpack.js.org">Absolute Link</a></li>
  <li><a href="//webpack.js.org">Protocol Relative Link</a></li>
  <li><a href="mailto:hello@example.com">Email Link</a></li>
  <li><a href="#hashtown">Hash Link</a></li>
</ul>
